Electronic devices, such as portable telephones, have recently had small sizes and high performance, and electronic components used in the electronic devices are required to have small sizes. Accordingly, these electronic devices and the electronic components have had low withstanding voltages. Upon being touched by a human body, an electrostatic pulse applies, to an electronic circuit of an electronic device, a high voltage ranging from several hundred volts to several kilovolts and having a rising time shorter than one nanosecond, and may break an electronic component.
In order to protect the electronic component from breaking, an electrostatic discharge (ESD) protector is connected between a line receiving the electrostatic pulse and the ground. A signal transmission line has had a high transmission speed higher than several hundred megabits per second. Upon having a large stray capacitance, the ESD protector may degrade signal quality. In order to protect an electronic component operating at a high transmission speed higher than several hundred megabits per second from breaking, the ESD protector is required to have a capacitance equal to or smaller than 1 pF.
Each of Patent Documents 1 and 2 discloses a conventional ESD protector including an overvoltage protective material filling a gap between two electrodes facing each other. When an excessive voltage caused by static electricity is applied between the electrodes, a current flows between conductive particles or semiconductor particles dispersed in the overvoltage protective material. Thus, the ESD protector allows the current flowing due to the excessive voltage to bypass the electronic component and flow to the ground.
In the conventional ESD protector, if the applied voltage is higher than 15 kV, an electrostatic discharge generates a large repulsive force, and may chip a protective resin layer covering the overvoltage protective material and cause the protector to break.
In order to lower a peak voltage applied to the ESD protector and improve characteristics of suppressing electrostatic discharge, it is required that a gap is precisely narrow. In the conventional ESD protector disclosed in Patent Document 1, the gap between the electrodes is formed by a photolithography technique and an etching process based mainly on chemical reactions. This method may cause the gap to have a width smaller than a predetermined width due to foreign matter attached to the gap at light exposure, or insufficient development, or insufficient etching.
The conventional ESD protector disclosed in Patent Document 1 is provided by forming electrodes and functional elements on an insulating substrate having a sheet shape, and then, dividing the insulating substrate into strips or separate pieces by a dicing technique. This dividing process may produce burrs on the divided surfaces, thus preventing ESD protectors from having small sizes stably.
In the conventional ESD protector disclosed in Patent Document 2, a gap is formed by cutting an electrode with laser. Since the electrode has a thickness ranging approximately from 10 to 20 μm, a high laser output is necessary for reliably cutting the electrode to form the gap precisely, thus preventing the gap from having a narrow width precisely.
Patent Document 1: JP 2002-538601A
Patent Document 2: JP 2002-015831A